The deleterious effects of detonation and hydrolock are well documented. Hydrolock is a condition in which water, oil, fuel, or some other incompressible liquid may be ingested or otherwise introduced into an engine cylinder, with the consequence of reducing the volume available in the cylinder within which air may be compressed when the engine is running. The reduction in cylinder volume available for air compression causes compression within the cylinder to reach higher-than-normal operating pressure and, in extreme cases, may cause internal components to fail. Hydrolock is most commonly experienced in conditions of extreme wetness, such as passenger automobiles driving upon flooded city streets, all terrain vehicles operating in swamp or river conditions, and watercraft operating in marine environments. Less well known, however, is the incidence of hydrolock in aircraft engines, particularly in radial-style engines in which one or more cylinders are oriented xe2x80x9cupside down,xe2x80x9d with the cylinder head being lower than the head of the piston, when the aircraft is in its normal xe2x80x9cuprightxe2x80x9d position. When a radial engine has been at rest for more than a few hours, oil and fuel may trickle down to the lowest point, which may be at the extreme xe2x80x9cupperxe2x80x9d end of one of the xe2x80x9cupside downxe2x80x9d cylinders, thereby reducing the cylinder volume available for the fuel-air mixture. If the engine should thereafter be started, compression within those cylinders may exceed design parameters and engine components may be bent or severely weakened. Although the engine damage may not immediately be evident, those components may thereafter fail during normal flight, resulting in an airborne engine failure and a life threatening emergency. Instances of hydrolock in other vehicles may be less serious, from a survival perspective, but nevertheless can result in extreme inconvenience if engine failure should occur at a location that is remote from engine repair or tow facilities. At a minimum, a hydrolock-induced engine failure will normally require an expensive engine rebuild.
Detonation is conceptually different from hydrolock, yet may produce a similar condition of excessive cylinder pressure that could damage engine components. Detonation occurs when the temperature within a cylinder causes the fuel-air mixture to auto-ignite whereupon the fuel-air mixture does not burn with a propagating wave front, but literally explodes, causing an instantaneous rise, then fall, in temperatures and pressures. Where the fuel-air mixture does not burn so as to propagate a moving wave front, the energy of the chemical reaction is dissipated before the piston can respond, and the energy available to force the piston downward is lost to irreversibilities including heat transfer and sound generation. The causes for this condition may vary from such conditions as an improper fuel-air mixture to a timing failure that causes a premature spark from the spark plug. Detonation has also been identified as a cause of aircraft engine failures, particularly where the fuel-air mixture, which may be controlled by the pilot, is set to run too lean when the aircraft is at cruise altitude. As with hydrolock, a detonating aircraft engine may fail during flight, again giving rise to an emergency of life-threatening proportions. A common result of detonation is excessive temperature that causes damage to the piston, rings, and valves, and excessive pressure.
One method of relieving excessive pressure in an engine cylinder is to allow pressure to vent through a deformable spark plug. As the temperature and pressure combine to create destructive conditions within a cylinder, a specially designed portion of the spark plug gives way to form a vent passage to the atmosphere, thereby allowing the excessive pressure to dissipate before components fail. This system is exemplified in U.S. Pat. No. 5,799,634 to Shifflette, entitled Spark Plug for Venting Excessive Pressure. The solution provided by Shifflette works well in environments in which the vent passage provided by the spark plug deformation is satisfactory both in size and location. That system, however, is not suitable for use in internal combustion engines that do not use a spark plug, nor in situations in which a larger or smaller hole than is provided by a spark plug is desired. In addition, when the spark plug of Shifflette deforms, the solid ejected portion may present an undesirable condition, either by being uncontrollably released within an engine compartment, or in extreme circumstances, penetrating the walls of the engine compartment and being released as a flying object that could cause damage external to the engine compartment. Another drawback is that the vent passage through a spark plug could vent cylinder contents against some other critical engine component such as a spark plug wire leading to another cylinder, a fuel line, a throttle linkage, or the like. Because spark plugs are normally installed with turning wrenches, it may not be possible to predict in advance the final orientation of the spark plug, hence the direction in which cylinder contents will vent. Where a vent passage has been created, it is possible that hot cylinder gases may be discharged against other critical components, causing those components to fail. Accordingly, what is needed is a cylinder pressure release system that is responsive to excessive engine pressures and temperatures, and that is able to be positioned wherever desired within an engine cylinder.
In accordance with this invention, a venting passageway may be created having an internal terminus within an engine cylinder and extending through the surrounding material in which the cylinder is formed, either the engine block or cylinder head. The external terminus of the passageway may be located within an engine cavity, such as, for example, an exhaust port, or may be located at an external surface of the engine. The external terminus will preferably be situated in a location where ejected solids may be contained and controlled. The passageway is hermetically closed with a mechanical sealing element of known strength and temperature limits. The sealing element may have component parts or an internal structure, and is responsive to pressure and temperature developed with the cylinder. The sealing element may be secured within the passageway by any one of a variety of sealing mechanisms including a press fit, a threaded shaft, a keyed shaft, a glue, epoxy, or other adhesive, or by other, equivalent securing means known within the art. As used herein, the term xe2x80x9csealing elementxe2x80x9d refers to the device used to seal the vent passageway and also includes securing means. Under conditions of excessive temperature, the sealing element, or portions thereof, will weaken to reduce the threshold pressure that will be required to create a vent passageway through the element. At any given temperature, cylinder pressure which stresses the sealing element beyond its strength will cause the sealing element to deform or dislodge such that the passage remains open thereafter. Combinations of cylinder temperature, combustion gas temperature, and combustion pressure may also act collectively or individually to cause the sealing element to release and allow venting of the passageway. As used herein, all designed failure modes of a sealing element to create an opening in the passageway sufficient to vent cylinder contents shall be referred to as a xe2x80x9crelease.xe2x80x9d Because a pressure relief passageway protects only a single cylinder, detonation in that cylinder may be prevented while still permitting acceptable power output from the remaining cylinders in a multiple cylinder engine. In all cases, after the sealing element has released, the engine may be restored to full functionality simply be replacing the sealing element with a new sealing element in the vent passageway and correcting the condition that caused the passageway to open.